Trump said he talked about the ban a lot during the campaign and "we're now putting it into effect."
In a pair of separate actions, Trump took steps to begin restructuring the White House National Security Council and the Homeland Security Council. He also gave Defense Secretary Jim Mattis and the Joint Chiefs of Staff, the president's top military advisers, 30 days to come up with a plan defeat the Islamic State group. Scores of people have been killed in terrorist acts that IS has carried out overseas or has inspired on U.S. soil.
Under an executive order that Trump signed in the presence of the news media, every political appointee joining the executive branch on or after Jan. 20 — the day Trump took office — must agree to the lobbying bans. That includes avoiding, for five years after leaving, lobbying the agency they worked for.
Another provision sets a two-year period during which appointees must avoid working on issues involving former employers or clients.
Trump is allowed to waive any of the restrictions.
Questions had been raised about how the bans would be enforced. The order says they are "solely enforceable" by the U.S. government "by any legally available means," including debarment proceeding within any affected executive branch agency, or civil court proceedings.
Former appointees who are found to have violated the ban may also be barred from lobbying their former agency for up to five years, on top of the five-year period covered by the pledge, the executive order states.
Trump said the order supersedes one that President Barack Obama signed on Jan. 21, 2009, that banned anyone from lobbying the government for a period of two years after leaving. Trump said Obama's order was "full of loopholes."
The president signed the order and a pair of presidential memoranda near the end of an intense day of telephone diplomacy during which he discussed a range of issues with the leaders of Japan, Germany, Russia, France and Australia. All are leaders Trump needs to build relationships with.
Trump had released the plan for a lobbying ban a few weeks before the November election, one of several promised policies aimed at curbing corruption and the influence of lobbyists in Washington. Trump also made promises about transparency and ethics.
Some have argued that the ban could make it difficult for Trump to fill thousands of jobs throughout the administration by causing some candidates to become squeamish about limiting their ability to make money after they leave government employment.
Others say the prohibitions on lobbying are too insignificant to be effective.